Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the computer in your car has detected a problem with the fuel injector for cylinder 9. It's like the injector's wires are mixed up with the coil's wires, causing a problem.
The vehicle's engine control module (ECM) has detected that the electrical circuit for the high-pressure fuel injector on cylinder 9 is shorted to the coil circuit.
The P31FC code indicates that there is an electrical fault in the high-pressure injector circuit for cylinder 9. Specifically, the low side of the injector circuit is shorted to the coil circuit, which can cause improper fuel delivery and engine performance issues.
• Engine misfire
• Poor fuel economy
• Check engine light illuminated
• Damaged wiring or connectors
• Faulty fuel injector
• Malfunctioning engine control module (ECM)
ECM: Engine Control Module, the computer that controls engine functions.
Injector: A device that sprays fuel into the engine's cylinders.
• Inspect wiring and connectors for damage or corrosion.
• Test the fuel injector for proper resistance.
• Check the ECM for faults or damage.
• Repair or replace damaged wiring or connectors.
• Replace the faulty fuel injector.
• Reprogram or replace the ECM if necessary.
• Multimeter
• OBD-II scanner
• Basic hand tools
$200 - $600
Moderate
• BMW 7 Series
• Mercedes-Benz S-Class
• Audi A8
• Regular maintenance checks
• Timely replacement of worn-out components
• Use quality fuel to avoid injector clogging
Engine Performance
• Avoid driving the vehicle until repaired to prevent further damage.
• Consult a professional mechanic for accurate diagnosis and repair.
Check vehicle warranty for coverage on engine components.
This code is relatively uncommon and typically associated with luxury vehicles with advanced fuel injection systems.
High – This issue can lead to engine performance problems and should be addressed promptly.
Driving with an engine misfire can be dangerous and may cause further damage to the vehicle.
• Engine at operating temperature
• Vehicle in a safe, stationary position
The fuel injector for cylinder 9 is located on the engine block, typically on the side or top, depending on the engine design.
Q: Can I drive with a P31FC code?
A: It's not recommended to drive with this code active, as it can cause engine misfires and further damage.
Q: How do I know if my fuel injector is bad?
A: Symptoms of a bad injector include engine misfires, poor fuel economy, and a rough idle.
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Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
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Universal · Wire connectors and repair kit
Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
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Fitment Required · Vehicle-fitment part
Commonly relevant for misfire, ignition-efficiency, and some drivability-related repairs.
Misfire and ignition-related faults commonly involve spark plugs as part of the repair path.
Check the correct plug type, gap, and engine application for your vehicle.
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Fitment Required · Vehicle-fitment part
Relevant when the fault points toward ignition-coil performance or cylinder-specific ignition issues.
Some ignition faults involve coil performance or cylinder-specific coil problems.
Match the coil to your engine and confirm the failed component before ordering.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.